1. Field of the Invention
The present invention relates to a camera, a bar code reader for the camera and a method of detecting bar code reading error. More particularly, the present invention relates to a medium-sized camera with a bar code reader for reading bar code provided on a Brownie film roll, and a method of detecting bar code reading error of the bar code reader.
2. Background Arts
ISO 120-type and 220-type rolled films are called Brownie film rolls in the art. In the 120-type, a 6 cm wide photo filmstrip is secured by an adhesive tape to a light-shielding paper which is longer than the filmstrip and backs the entire length of the filmstrip. The filmstrip is coiled with the backing paper around a spool. In the 220-type, short pieces of light-shielding paper are secured by adhesive tapes to opposite ends, i.e. leader and trailer, of a 6 cm wide photo filmstrip. Since the long backing paper is replaced by the short leader and trailer papers in the 220-type, a longer filmstrip, twice as long as the 120-type, is coiled around a spool in the 220-type. Unlike ISO-135 film rolls, the 120-type and 220-type film rolls are not contained in a cartridge shell. Hereinafter, the 120-type and 220-type film rolls will be referred to as the roll film.
Since the roll film is not provided with any device like DX code on the ISO-135 cartridge shell that allows the camera to read the film speed and the number of exposures available on each film roll, manual setup for adjusting the camera to the film speed is necessary after loading the roll film. The photographer should also calculate the remaining number of available exposures based on the initial number of available exposures and the number of accomplished exposures that is indicated by a count-up type frame counter. Where the camera is provided with a count-down type frame counter, the photographer must preset the frame counter to the initial number of available exposures.
An idea of providing a bar code on the adhesive tape connecting the filmstrip to the light-shielding paper is disclosed in U.S. patent application Ser. No. 08/712,387, now U.S. Pat. No. 5,845,869 that was filed based on Japanese Patent Applications No. 7-235127 et al. The bar code on the adhesive tape represents information about the roll film, such as the film speed, the film type and the number of available exposures, and is readable by a bar code reader having a reflective photo sensor.
For use in the camera, the bar code reader may not project light of the wavelength range the photo filmstrip is sensitive to, so that an infrared light emitting element, e.g. an infrared light emission diode, can only be used as a light source of the reflective photo sensor. In a case where the infrared light is projected directly toward the bar code, and the light receptive element receives reflected and diffused light directly from the bar code, the resolving power of this type photo sensor is relatively low, i.e. about 1.5 mm to 2.0 mm. Moreover, this type photo sensor is affected by light absorption or extinction factor of the black bar elements of the bar code.
On the other hand, since the adhesive tape, as well as the light-shielding paper and the filmstrip, is coiled around the spool, they are inevitably curled. According to the curl of the surface having the bar code thereon, the distance from the photo sensor can vary at most 1 mm or so. The variation in the distance adversely affects the accuracy of the photo sensor.
To prevent errors, it is desirable for the bar code on the roll film to make both the minimum width of the bar elements and the ratio of the maximum width to the minimum width as large as possible. According to the ISO standard for the roll film, the length of the adhesive tape in the lengthwise direction of the filmstrip is limited up to 25 mm. In order to scan the bar code while the roll film is advanced in the camera, the bar elements should be arranged side by side in the lengthwise direction of the filmstrip. To record requisite amount of information about the roll film by the bar code of this arrangement, the minimum width of the bar elements must be less than 1 mm.
In that case, a bar code reader using the reflective photo sensor having the above construction cannot accurately read the bar code. It is possible to use a photo sensor having a light projection lens and a light reception lens in front of light emitting and light receiving elements, for obtaining a higher resolving power. Because of the depth of focus of the lens system, this type photo sensor also has a larger capacity toward the variation in distance to the bar code. However, in comparison with the reflective photo sensor with no lens, the intensity of light received on the light receiving element is totally increased, and is more affected by the reflection factor of the surface on which the bar code is provided. Where the reflection factor of the surface having the bar code recorded thereon is high, the light reflected even from the black bar elements can be so high that it becomes difficult to discriminate between the black bar elements and the white bar elements.
Although it is possible to reduce the above problem by mounting the light emitting and receiving elements of the reflective photo sensor separately from each other and adjusting their relative positions and angles, this solution is not practical as for the photo sensor built in the mass-produced camera.
Moreover, since the adhesive tape is put only on the leading end of the filmstrip in the 120-type, the photo sensor scans the bar code only once during the preliminary loading of the roll film. Even if the bar code is stained, or damaged by wrinkles, the bar code reader is required to decode the bar code with accuracy based on the output signal from the photo sensor. Therefore, the bar code reader must be able to check if the output signal from the photo sensor includes any errors.